Uplink control signaling for joint FDD and TDD carrier aggregation

ABSTRACT

Embodiments of the invention are directed to a method for operating a mobile device including establishing a connection to a first base station designated as a PCell and establishing a connection to a second base station designated as a SCell. When the mobile device receives PDSCH from a TDD SCell in a subframe n, it transmits a HARQ ACK to an FDD PCell in subframe n+4. When the mobile device receives PDSCH in a downlink subframe from an FDD SCell, it transmits a HARQ ACK corresponding to the PDSCH to a TDD PCell in a selected uplink subframe. The selected uplink subframe may be the first valid uplink subframe following the downlink subframe. For example, where the downlink subframe carrying the PDSCH is subframe n, and the selected uplink subframe is subframe n+k, where k≧4.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/840,993, filed on Jun. 28, 2013,titled “Uplink Control Signaling for Joint FDD and TDD CarrierAggregation,” U.S. Provisional Patent Application No. 61/866,290, filedon Aug. 15, 2013, titled “Uplink Control Signaling for Joint FDD and TDDCarrier Aggregation,” and U.S. Provisional Patent Application No.61/868,970, filed on Aug. 22, 2013, titled “Uplink Control Signaling forJoint FDD and TDD Carrier Aggregation” the disclosures of which arehereby incorporated by reference herein in their entireties.

TECHNICAL FIELD

The technical field of this invention is wireless communication such aswireless telephony.

BACKGROUND

A cellular wireless network comprises multiple base stations, where eachbase station transmits to (downlink or DL) and receives from (uplink orUL) a plurality of mobile users in its coverage area. The explosion indata traffic in wireless cellular networks has created a need for rapidexpansion of network capacity to cope with increasing user demand.Carrier aggregation provides one method to increase network capacity.With carrier aggregation, a base station simultaneously transmits datato, or receives data from, mobile user equipment (UE) on multiplecarriers in the same or different RF bands. For example, in a cellularsystem complying with the Third Generation Partnership Project (3GPP)Long Term Evolution (LTE) standards, carrier aggregation has beenstandardized in LTE Releases 10 and 11 for both intra-band andinter-band operation. The cost of mobile UEs is strongly dependent uponthe cost of the RF front end, including the mixers, oscillators andradio amplifier, which is designed to work in a specific RF band(s). Tomaximize return on investment, mobile UE vendors strive for equipmentthat can be used in both Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) modes as well as in the most widely deployed RFbands across all geographic regions.

On the other hand, the cost of RF spectrum is a significant bottleneckin the deployment of ubiquitous and high data rate wirelesscommunication systems. Cellular network operators acquire RF spectrumbased on several factors including the size of allocated spectrum chunks(e.g., higher RF bands are better) and optimized coverage (e.g., lowerfrequency bands provide better in-building penetration). Furthermore,widespread adoption of a particular band guarantees that there would bemobile devices supporting that band. Based on these factors, a networkoperator may own spectrum in both FDD and TDD bands and may want toconfigure carrier aggregation for a UE on both TDD and FDD componentcarriers.

SUMMARY

The example embodiments described herein are directed to a joint FDD andTDD design that provides carrier aggregation in a wireless communicationsystem. The signaling methodology presented herein may be implemented inan Orthogonal Frequency-Division Multiplexing (OFDM)-based cellularsystem that operates in FDD and/or TDD modes, such as in an LTE cellularnetwork.

In one embodiment, a method for operating a mobile device is describedincluding establishing a connection to a first base station designatedas a primary serving cell (PCell) and establishing a connection to asecond base station designated as a secondary serving cell (SCell). TheSCell uses a different operating mode than the PCell. The PCell andSCell operating modes are selected from FDD and TDD modes. The mobiledevice receives subframe scheduling messages from the SCell in adownlink subframe and selects an uplink subframe to send a schedulingmessage acknowledgement based upon the operating mode of the PCell.

In one embodiment, the PCell operates in FDD mode and the SCell operatesin TDD mode. In this configuration, the mobile device receives aPhysical Downlink Shared Channel (PDSCH) from the TDD SCell in asubframe n and transmits a Hybrid Automatic Repeat Requestacknowledgment (HARQ ACK) to the FDD PCell in subframe n+4.

In another embodiment, the PCell operates in TDD mode and the SCelloperates in FDD mode. In this configuration, the mobile device receivesPDSCH in a downlink subframe from the FDD SCell and transmits a HARQ ACKcorresponding to the PDSCH to the TDD PCell in a selected uplinksubframe. The selected uplink subframe may be the first valid uplinksubframe following the downlink subframe. For example, where thedownlink subframe carrying the PDSCH is subframe n, and the selecteduplink subframe is subframe n+k, where k≧4.

The mobile device may operate in a half-duplex TDD mode in which case ituses an uplink/downlink subframe configuration for a TDD PCell whentransmitting to an FDD SCell.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in thedrawings, in which:

FIG. 1 illustrates a heterogeneous deployment scenario wherein a basestation operates in FDD mode and provides macro coverage in a macro cellsite having three sectors.

FIG. 2 shows a mobile device scheduled to transmit PUSCH on the FDDPCell in subframe 7 of radio frame n_(f)+1.

FIG. 3 illustrates the scenario where a mobile device is configured withan FDD SCell and a TDD PCell employing TDD UL/DL Configuration 2.

FIG. 4 illustrates use of an FDD secondary serving cell for half-duplexTDD mobile devices employing TDD UL/DL Configuration 1.

FIG. 5 illustrates usage of a TDD cell as a secondary serving cell for aFDD-only mobile device.

FIG. 6 is a block diagram illustrating internal details of a mobile userequipment and a base station operating in a network system such asillustrated in FIG. 1.

DETAILED DESCRIPTION

The invention(s) will now be described more fully hereinafter withreference to the accompanying drawings. The invention(s) may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention(s) to a person of ordinaryskill in the art. A person of ordinary skill in the art may be able touse the various embodiments of the invention(s).

Deployment Scenario for Joint FDD/TDD Carrier Aggregation

Joint FDD/TDD operation is proposed when a cellular network operatorowns both FDD and TDD spectrum in the same geographical area. Forexample, in a given geographical area, FDD spectrum at 800 MHz and TDDspectrum at 2.6 GHz may be available. FIG. 1 illustrates a heterogeneousdeployment scenario wherein base station 101 operates in FDD mode andprovides macro coverage in a macro cell site having three sectors102-104. Base stations 105 are low power nodes that operate in TDD modein a higher frequency band and control small cells 106. Small cells 106can be used as capacity boosters to increase throughput at hotspotswithin the macro-cell sectors. In other scenarios, the macro cell basestation 101 may operate in TDD mode and the hotspot base stations 105may operate in FDD mode. Base stations 101 and 105 may be owned andcontrolled by a single network operator or by two or more differentnetwork operators in a radio access network (RAN) sharing arrangement.

Given this general deployment scenario, there are three modes of jointFDD/TDD operation, namely, a default single mode operation, carrieraggregation, and inter-node aggregation as explained below.

In carrier aggregation (CA), a UE may be configured to receive andtransmit data on multiple component carriers (CCs). From the perspectiveof the MAC layer, data transmission in either DL-only or both DL and ULdirections are scheduled per component carrier (CC). As such, eachcomponent carrier may be considered as a serving cell each with its ownMAC scheduler. In the LTE system, an anchor cell provides a mobilityconnection to the network and is called the primary serving cell(PCell). Depending on data traffic requirements, the base station mayconfigure additional serving cells known as secondary serving cells(SCells). In one deployment configuration, all primary and secondaryserving cells are collocated. In a different deployment configuration,an SCell may be deployed at a different location from the PCell with abackhaul connection 107—preferably with low latency and highthroughput—connecting the PCell and SCell locations.

For joint FDD-TDD carrier aggregation operation, the PCell (and possiblysome SCells) may be FDD whereas one or more SCells may be TDD orvice-versa. The requirements for joint FDD-TDD carrier aggregationinclude:

-   -   UEs that are capable of multi-mode operation (i.e., operation as        either TDD or FDD UEs);    -   inter-band carrier aggregation capability;    -   UL carrier aggregation joint operation also requires the UEs to        support an independent UL timing advance for different component        carriers; and    -   determining the cell to which the UE transmits uplink control        information (UCI).

Joint FDD-TDD Carrier Aggregation Design.

Hybrid Automatic Repeat Request (HARQ) scheduling and feedbackconsiderations.

For an LTE system, some existing procedures and DL/UL signaling forcarrier aggregation are agnostic as to whether the configured servingcells operate in FDD or TDD modes. A key difference is the HARQscheduling and HARQ feedback acknowledgments (HARQ-ACK) timelines. Byvirtue of the paired DL and UL carriers in FDD, a UE may be scheduledfor DL assignments and/or UL grants with one-millisecond granularity(i.e., in any subframe). Correspondingly, the HARQ-ACK feedback for a DLassignment in subframe n is transmitted in subframe n+4 for normal HARQoperation. Similarly, the DL HARQ-ACK feedback for an UL grant insubframe n is transmitted on the Physical HARQ Indicator Channel (PHICH)in subframe n+4.

On the other hand, TDD divides a radio frame into DL and UL subframeswith a Guard Period to enable transition from DL to UL. This results inrestricted opportunities for DL/UL transmission and HARQ-ACK feedback.The LTE system defines a Special subframe which consists of a DL portion(the Downlink Pilot Time Slot or DwPTS), a Guard Period, and an ULportion (the Uplink Pilot Time Slot or UpPTS).

There are seven TDD UL/DL configurations defined in LTE Releases 8-11 asshown in Table 1. The choice of the TDD UL/DL configuration for a givencell depends on several factors, such as the DL and UL traffic ratesobserved in a cell, the need for good UL coverage (e.g., requiring anUL-heavy UL/DL configuration), and coexistence with other TDD wirelesstechnologies such as Time Division Synchronous Code Division MultipleAccess (TD-SCDMA).

TABLE 1 DOWNLINK- UPLINK- TO-UPLINK DOWNLINK SWITCH-POINT SUBFRAMENUMBER/TYPE CONFIGURATION PERIODICITY 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U UU D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10ms  D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D DD D D D D 6 5 ms D S U U U D S U U D

As can be seen in Table 1, when operating in TDD mode, there are limitedUL subframes in which to transmit data or uplink control information,such as HARQ-ACK feedback, channel state information (CSI), andscheduling requests. In an UL subframe, the UE may be required totransmit HARQ-ACK feedback for a set of M DL subframes, which isreferred to as the Downlink association set.

Table 2 represents the HARQ-ACK DL association set K for TDD UL/DLconfigurations in an LTE system. The set of possible HARQ-ACK feedbackstates includes positive acknowledgement (ACK), negative acknowledgement(NACK), and Discontinuous Transmission (DTX). Therefore, given a set ofM elements, {k₀, k₁, . . . , k_(M−1)} the UE generates HARQ-ACK feedbackin a UL subframe n corresponding to DL subframes {n−k₀, n−k₁, . . . ,n−k_(M−1)}. The Downlink Control Information (DCI) formats scheduling DLassignments or UL grants on a TDD serving cell contain a DownlinkAssignment Index (DAI) field which indicates to the UE the number of DLsubframes for which HARQ-ACK feedback is expected. For example, in an ULsubframe n for which up to M DL subframes {n−k₀, n−k₁, . . . , k_(M−1)}may require HARQ-ACK feedback, the DAI field may indicate that fewerthan M subframes were actually scheduled to the UE. A radio frameincludes ten subframes labeled as subframes 0 to 9. In Table 2, thesubframes in subsequent frames may be labeled as subframes 10 to 19,etc. in order to compute the subtraction n−k_(i) for i=0 to M−1.

TABLE 2 UL/DL SUBFRAME n CONFIGURATION 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, 4, 11, 6 — — — — — — — 6 — — 7 7 5 — —7 7 —

A design constraint for carrier aggregation in current LTE systems isthat UCI is only transmitted on the Physical Uplink Control Channel(PUCCH) of the PCell. Therefore, efficient FDD-TDD HARQ-ACK feedback incarrier aggregation depends on which duplex mode is operated on thePCell (i.e., FDD is full-duplex, and TDD is half-duplex). Certain designprinciples used in current LTE systems may be re-visited for moreefficient FDD-TDD operation. These include:

-   -   introduce no new TDD UL/DL configurations for joint FDD-TDD        carrier aggregation operation; and    -   transmit UCI only on the PUCCH of the PCell.

In the following sections, different HARQ-ACK feedback designs areconsidered for the cases where the PCell is operating in either FDD orTDD mode. Although these examples are described using the special caseof a single SCell, it will be understood that the design may begeneralized to carrier aggregation using multiple SCells.

PCell in FDD Mode, and SCell in TDD Mode.

When the network includes a mix of FDD and TDD cells, one benefit ofhaving the PCell operate in FDD mode is that all subframes of a FDDradio frame are valid UL subframes for UCI transmission. Therefore, whenan additional serving cell is configured for TDD, the HARQ-ACK feedbacktimeline for any TDD UL/DL configuration can be followed for HARQ-ACKfeedback on PUCCH because the set of UL subframes for the PCell is asuperset of the TDD UL subframes. For single duplex mode carrieraggregation, an LTE Release 10 or Release 11 UE may be configured withone of the following PUCCH schemes: PUCCH Format 1b with channelselection or PUCCH Format 3. The same PUCCH schemes may be configuredfor FDD-TDD CA as follows

1) If the UE detects a DL assignment on the Physical Downlink ControlChannel (PDCCH) or Enhanced Physical Downlink Control Channel (EPDCCH)scheduling PDSCH in a TDD SCell in any one of the M subframes associatedwith an uplink subframe.

-   -   a) When PUCCH Format 3 is configured, the PUCCH resource is        indicated by the Transmit Power Control (TPC) field of the PDCCH        scheduling PDSCH on the SCell, where the TPC field indicates one        out of four semi-statically configured resources.    -   b) When PUCCH Format 1b with channel selection is configured for        the case of a single SCell:        -   if the PDSCH on the SCell is cross-scheduled from the PCell,            up to two resources may be indicated by dynamic PUCCH            allocation based on the PDCCH/EPDCCH detected on the PCell;        -   otherwise, if the PDSCH is self-scheduled on the SCell, the            value of the TPC field of any PDCCH/EPDCCH scheduling PDSCH            in any of the M DL subframes associated with the UL subframe            indicates one of a set of four pairs of semi-statically            configured PUCCH resources.

2) If the UE does not detect a PDCCH/EPDCCH scheduling PDSCH in a TDDSCell in any one of the M subframes associated with an uplink subframe,then the UE transmits on the PUCCH of the FDD PCell in subframe n onlyif a PDSCH or PDCCH/EPDCCH indicating Semi-Persistent Scheduling (SPS)release is detected in the PCell in subframe n−4.

It is also possible to optimize HARQ-ACK feedback for a TDD SCell whenthe PCell is operated in FDD mode. Specifically, the HARQ-ACK timing forthe PDSCH transmitted on the TDD SCell follows the HARQ-ACK timing onthe FDD PCell. Thus, the UE transmits HARQ-ACK feedback in the PUCCH ofthe PCell in subframe n for a PDSCH detected on a TDD SCell in subframen−4. When PUCCH Format 3 is configured, the PUCCH resource is indicatedby the TPC field of the PDCCH/EPDCCH scheduling PDSCH on the TDD SCell.Similarly, when PUCCH Format 1b with channel selection is configured upto two PUCCH resources corresponding to SCell PDSCH are indicated by theTPC field of the PDCCH/EPDCCH scheduling the PDSCH on the SCell. It isnoted that this scheme eliminates the need for a Downlink Associationset (i.e., M=1 for any UL/DL configuration). Therefore, there is no needto include DAI field in the DCI formats scheduling a DL assignment or ULgrant on a TDD SCell when the PCell operates in FDD mode because theHARQ-ACK timing follows the FDD PCell HARQ-ACK timing.

HARQ-ACK Transmission on PUSCH.

Another consideration is how to multiplex the HARQ-ACK bits on PUSCHwhen the UE is transmitting on PUSCH. In LTE Release 11 TDD, the numberof HARQ-ACK bits transmitted on PUSCH for a configured serving celldepends on the size of the DL association set M or the DAI valuecontained in the DL assignment or in the UL grant that is transmitted onthe PDCCH/EPDCCH. Zero to nine subframes may be indicated by the DAIvalue in the PDCCH/EPDCCH. In contrast, for an FDD serving cell in LTERelease 11 the number of HARQ-ACK bits is based on the number ofconfigured serving cells and the downlink transmission modes configuredfor each FDD serving cell.

FIG. 2 illustrates carrier aggregation with a PCell in FDD mode and anSCell in TDD UL/DL Configuration 2. In the TDD SCell, DL assignments forthe SCell in DL subframes 4 and 5 of radio frame n_(f) are acknowledged(HARQ-ACK feedback) by the UE in UL subframe 2 of radio frame n_(f)+1.The DL assignment for the SCell in Special subframe 1 of radio framen_(f)+1 is acknowledged by the UE in UL subframe 7 of radio framen_(f)+1. Conversely, in the FDD PCell, because it has a pair of CCs forDL and UL respectively, each DL subframe n can always be uniquelyassociated with a corresponding UL subframe that is four subframes later(n+4). For example, a DL assignment in subframe 8 of radio frame n_(f)is acknowledged in UL subframe 2 of radio frame N_(f)+1. Furthermore, ifan UL grant is transmitted in subframe 8 of radio frame n_(f) inaddition to the DL assignment, the UE transmits the HARQ-ACK feedback onPUSCH if the UE is not configured for simultaneous PUCCH and PUSCHtransmission. There is no need for a DAI field in FDD since the feedbackin an UL subframe n+4 corresponds to the DL assignment transmitted onthe PDSCH in DL subframe n.

For joint FDD-TDD carrier aggregation operation, HARQ-ACK feedback onPUSCH may need to take into account HARQ-ACK feedback for FDD cells.However, in current FDD-only carrier aggregation operation, there is noDAI field in the Downlink Control Information (DCI) formats. Therefore,there is no mechanism to indicate that two possible solutions aredescribed below to efficiently support joint FDD-TDD carrier aggregationoperation.

Scheme 1: maintain the current design in which there is no DAI field forDCI formats in an FDD cell.

1) For PUSCH transmission on an FDD serving cell:

-   -   a) Arrange the HARQ-ACK bits according to the serving cell        index, where 0 is for the PCell, 1 is the first SCell, etc.    -   b) For an FDD cell, generate one or two HARQ-ACK bits depending        on whether the configured transmission mode supports one or two        transport blocks, respectively.    -   c) For the C^(th) TDD cell, generate either B_(c) ^(DL) or        2B_(c) ^(DL) depending on whether the configured transmission        mode supports one or two transport blocks respectively, where        B_(C) ^(DL)=M.

In an alternative embodiment, the UE determines the HARQ-ACK feedbackfor a TDD SCell based on the value of the DAI (V_(DAI) ^(DL)) in themost recent detected PDCCH/EPDCCH scheduling PDSCH on the SCell for theDL association set {n−k_(m)}, m=0, . . . , M−1. Thus, the number ofgenerated HARQ-ACK bits for this TDD cell is B_(c) ^(DL)=V_(DAI) ^(DL).

-   -   d) An example is shown in FIG. 2 for an SCell using TDD UL/DL        Configuration 2. In UL subframe 2 of radio frame n_(f)+1, the UE        shall transmit HARQ-ACK feedback corresponding to detected DL        assignments in subframes 4 and 5 of the TDD SCell and subframe 8        of the FDD PCell in radio frame n_(f).

2) For PUSCH transmission on a TDD serving cell:

-   -   a) If the PUSCH transmission is not adjusted based on a detected        PDCCH/EPDCCH with DCI format 0/4, then follow the same bit        ordering and number of generated bits as above for PUSCH        transmission on an FDD serving cell with B_(c) ^(DL)=M.    -   b) If the PUSCH transmission is adjusted based on a detected        PDCCH/EPDCCH conveying UL DCI format 0/4, then        -   i) For the c^(th) TDD cell, B_(c) ^(DL)=W_(DAI) ^(UL) where            W_(DAI) ^(UL) is the DAI value in the detected DCI format            0/4.        -   ii) In one embodiment, the bit ordering is determined            according to the cell index as described above for PUSCH            transmitted on an FDD serving cell.        -   iii) In another embodiment, the HARQ-ACK bits generated for            one or more FDD serving cells are appended to the HARQ-ACK            bits for the TDD serving cells (i.e., they are the least            significant bits (LSBs)). Therefore, when a UL grant is            detected for subframe n on a TDD serving cell, if there was            no PDSCH or SPS release DCI in subframe n−4 of the FDD            serving cell, the bit mapping is the same as for TDD-only            carrier aggregation.

Scheme 2: add a DAI field for DCI formats in an FDD serving cell. TheDAI field would indicate to the UE the total number of subframesrequiring feedback for any configured TDD serving cell. This solutionavoids any possible ambiguity between the base station and the UE incase the UE misses all the scheduling assignments within the DLassociation set for a UL subframe n. This scheme is also applicable fora TDD PCell and a FDD SCell because an UL grant for the FDD SCell maycontain a DAI field to indicate the number of DL subframes of the TDDPCell that require HARQ-ACK feedback.

The length of the DAI field may be two bits, for example, but in otherembodiments a one-bit DAI field may be defined. The DAI field is used toindicate to the UE that feedback is required for at least one configuredTDD serving cell with B_(c) ^(DL)=M. It will be understood that othervalues are not precluded as the main goal here is to inform the UE whentransmitting PUSCH in an FDD cell to include HARQ-ACK feedback for TDDcells.

This scheme is also applicable for a TDD PCell and a FDD SCell becausean UL grant for the FDD SCell may contain a DAI field to indicate thenumber of DL subframes of the TDD PCell that require HARQ-ACK feedback.Therefore, the DAI field may be present for PDCCH/EPDCCH on a FDDserving cell whenever at least one TDD serving cell is configured for aUE.

Alternatively, the DAI field is only present for an FDD serving cellwhen the subframe is also an UL subframe corresponding to a linked DLassociation set for at least one of the configured TDD serving cells.

FIG. 2 shows that the UE is scheduled to transmit PUSCH on the FDD PCellin subframe 7 of radio frame nf+1. There is also a DL assignment insubframe 1 (special subframe) of the TDD SCell in the same frame. Evenif the UE misses this DL assignment, the value of the DAI field in theUL grant for UL subframe 7 shall indicate to the UE how many DLsubframes required HARQ-ACK feedback. This mechanism enables the UE todetermine that it failed to detect one or more DL assignments on the TDDserving cell.

PCell in TDD Mode, and SCell in FDD Mode.

An interesting deployment scenario occurs when the PCell is operating inTDD mode and at least one SCell is operating in FDD mode. If the designconstraint that PUCCH transmission only occurs on the PCell is followed,this limits HARQ-ACK feedback opportunities for the FDD SCell.Essentially, it forces the FDD SCell to follow the TDD PCell HARQ-ACKfeedback timeline. For the case of a DL-only FDD serving cell without apaired UL carrier, this is the default operation. However, when there isa paired UL carrier for the FDD serving cell, it makes sense to considermore efficient means for transmitting HARQ-ACK feedback corresponding toPDSCH on the FDD SCell. This consideration is even more imperative forthe following scenario.

FIG. 3 illustrates the scenario where a UE is configured with an FDDSCell and a TDD PCell employing TDD UL/DL Configuration 2. Consider thecase where a UE is scheduled for PDSCH reception in a DL subframe of theFDD SCell but this subframe is an UL subframe according to the TDD UL/DLconfiguration of the PCell as illustrated in FIG. 3, for example.Following current FDD procedures the UE should transmit thecorresponding feedback in subframe 6, but subframe 6 is a Specialsubframe for the TDD PCell. One solution to this problem is to configurethe UE to transmit HARQ-ACK feedback on the PUCCH of the SCell. Thereare two possible implementations of this solution:

-   -   simultaneous PUCCH-PUCCH transmission on both PCell and SCell;        or    -   time-multiplexed PUCCH transmission. For this scheme the UE        transmits PUCCH on the FDD SCell only if the UL subframe on the        SCell corresponds to a DL subframe on the TDD PCell. Otherwise,        if the subframe is an UL subframe for both FDD and TDD serving        cells, PUCCH shall be transmitted on the PCell.

An alternative solution would be to schedule the HARQ-ACK feedbackcorresponding to a DL assignment on the FDD SCell to be transmitted inthe first valid UL subframe of the TDD PCell. Specifically, for a PDSCHdetected in subframe n on the FDD SCell, the UE shall transmit thecorresponding HARQ-ACK feedback in the first valid UL subframe n+k wherek≧4. In the example illustrated in FIG. 3, the HARQ-ACK feedback istransmitted in subframe 7 on the PCell.

Considerations for CSI Reporting.

Aperiodic or periodic CSI reporting may be configured in a mannersimilar to the case of single duplex mode carrier aggregation. Forperiodic CSI reporting, the priority of CSI reports is based on PUCCHreporting types and serving cell index. When the PCell operates in TDDmode, some restrictions may be placed on the Channel Quality Indicator(CQI)/Precoding Matrix Indicator (PMI) reporting period of a FDD SCelldepending on the TDD UL/DL Configuration of the PCell. For example, ifthe PCell uses UL/DL Configuration 5, reporting periodicity oftwo-milliseconds may imply frequent dropping of CSI reporting for theFDD SCell. Therefore, if the periodic CSI reporting occasion or subframecoincides with a DL subframe on the TDD PCell, the UE shall not transmitthe CSI report.

Considerations on UE Capability.

In general, full duplex capability is required for a UE that supportsFDD-TDD carrier aggregation. However, it is possible to allow ahalf-duplex UE to enjoy some of the benefits of FDD-TDD CA. For example,an LTE Release 11 TDD UE that is Radio Resource Control (RRC)-connectedon a TDD serving cell can be configured to receive PDSCH on a secondaryserving cell that uses the same TDD UL/DL configuration as the primaryserving cell. If the SCell is operating in FDD mode, the UE may beconfigured to apply the same UL/DL configuration of the TDD PCell.

FIG. 4 illustrates usage of an FDD secondary serving cell forhalf-duplex TDD UEs employing TDD UL/DL Configuration 1. As shown inFIG. 4, subframes {2, 3, 7, 8} and {0, 1, 4, 5, 6, 9} are not valid DLor UL subframes respectively for the half-duplex TDD UE on the FDDSCell. Although this subframe restriction may initially seem to be awaste of network resources, it is noted that the base station can assignother UEs (e.g., either FDD UEs or other TDD UEs with full-duplexcapability) to the unused resources. Moreover, the performance of a UEwith half-duplex capability is similar to TDD-only carrier aggregationwherein the same UL/DL configuration is configured on each serving cell.

In a similar manner, it is possible for a UE that only supports FDDduplex mode to be configured to receive Downlink Shared Channel (DL-SCH)data on the PDSCH of a SCell, where the SCell is actually deployed on aTDD carrier. This scenario is possible when an FDD band overlaps infrequency with a TDD band. For example, 3GPP Band 7 is an FDD band thatoverlaps in frequency with 3GPP TDD Band 41. An operator with spectrumin this RF region may choose to operate either as a TDD or FDD carrier.When operated as a TDD carrier, an FDD-only UE can be configured toreceive data on this carrier by configuring the UE with a restricted setof subframes that matches the DL subframes on the TDD carrier.

FIG. 5 illustrates usage of a TDD cell as a secondary serving cell for aFDD-only UE. The UE may be configured with a bit map that indicateswhich subframes it should monitor for DL-SCH data. Frame (a) in FIG. 5illustrates an example in which a TDD carrier is configured to operatein UL/DL Configuration 1. An FDD-only UE may be configured with asecondary serving cell on this TDD component carrier. Traditionally, theFDD-only UE monitors all subframes in a radio frame for DCI transmittedon the PDCCH or EPDCCH. However, for this TDD carrier, there is no needfor the FDD-only UE to waste energy monitoring for DCI on thePDCCH/EPDCCH that cannot be transmitted in subframes {2, 3, 7, 8}because those subframes are designated for UL. Therefore, the FDD UE isconfigured with a bit map specifying a restricted set of subframes tomonitor for DCI.

As illustrated in frame (b) in FIG. 5, the FDD-only UE monitors forDL-SCH data from the SCell on a restricted set of subframes {0, 4, 5,9}. The bit map designating this restricted set of subframes may besemi-statically configured by RRC signaling.

In a different embodiment of the invention the UE can be configured withan extended bit map indicating not only subframes where to monitor forDCI, but also subframes where a detected DL assignment on the PDSCH islimited to fewer OFDM symbols than the maximum number of OFDM symbols inthe subframe. This allows the UE to receive PDSCH on special subframes.For example, when a TDD cell applies normal cyclic prefix in thedownlink, Special Subframe Configuration 11 contains 11 OFDM symbols.Therefore, the FDD-only UE is configured to receive a DL assignment inthis subframe up to the 11th OFDM symbol.

Frame (c) in FIG. 5 illustrates a restricted set of subframes thatincludes the Special subframes {1, 6}. An FDD-only UE may be configuredto receive data on less than the total number of OFDM symbols in theSpecial subframes.

In either embodiment (i.e., using a restricted set of subframes thatincludes just DL subframes or includes DL and Special subframes), theHARQ-ACK timeline should follow the FDD procedure if the UL carrier isFDD. For example, when a DL assignment is received in subframe n, the UEtransmits the HARQ-ACK feedback in subframe n+4.

FIG. 6 is a block diagram illustrating internal details of a mobile UE601 and a base station 603, such as an eNB, operating in a networksystem such as illustrated in FIG. 1. Mobile UE 601 may communicate withmultiple base stations 603 in a carrier aggregation operation. Mobile UE601 may represent any of a variety of devices such as a server, adesktop computer, a laptop computer, a cellular phone, a PersonalDigital Assistant (PDA), a smart phone or other electronic devices. Insome embodiments, the electronic mobile UE 601 communicates with eNB 602based on a LTE or Evolved Universal Terrestrial Radio Access (E-UTRA)protocol. Alternatively, another communication protocol now known orlater developed can be used.

Mobile UE 601 comprises a processor 603 coupled to a memory 604 and atransceiver 605. The memory 604 stores (software) applications 606 forexecution by the processor 603. The applications could comprise anyknown or future application useful for individuals or organizations.These applications could be categorized as operating systems (OS),device drivers, databases, multimedia tools, presentation tools,Internet browsers, emailers, Voice-Over-Internet Protocol (VOIP) tools,file browsers, firewalls, instant messaging, finance tools, games, wordprocessors or other categories. Regardless of the exact nature of theapplications, at least some of the applications may direct the mobile UE601 to transmit UL signals to eNB (base station) 602 periodically orcontinuously via the transceiver 605.

Transceiver 605 includes uplink logic which may be implemented byexecution of instructions that control the operation of the transceiver.Some of these instructions may be stored in memory 604 and executed whenneeded by processor 603. As would be understood by one of skill in theart, the components of the uplink logic may involve the physical (PHY)layer and/or the Media Access Control (MAC) layer of the transceiver605. Transceiver 605 includes one or more receivers 607 and one or moretransmitters 608.

Processor 603 may send or receive data to various input/output devices609. A subscriber identity module (SIM) card stores and retrievesinformation used for making calls via the cellular system. A Bluetoothbaseband unit may be provided for wireless connection to a microphoneand headset for sending and receiving voice data. Processor 603 may sendinformation to a display unit for interaction with a user of mobile UE601 during a call process. The display may also display picturesreceived from the network, from a local camera, or from other sourcessuch as a Universal Serial Bus (USB) connector. Processor 603 may alsosend a video stream to the display that is received from various sourcessuch as the cellular network via RF transceiver 605 or the camera.

eNB 602 comprises a processor 610 coupled to a memory 611, symbolprocessing circuitry 612, and a transceiver 613 via backplane bus 614.The memory stores applications 615 for execution by processor 610. Theapplications could comprise any known or future application useful formanaging wireless communications. At least some of the applications 615may direct eNB 602 to manage transmissions to or from mobile UE 601. eNB602 may operate in a FDD or TDD mode and may communicate with other basestations (not shown) for carrier aggregation.

Transceiver 613 comprises an uplink resource manager, which enables eNB602 to selectively allocate uplink Physical Uplink Shared CHannel(PUSCH) resources to mobile UE 601. As would be understood by one ofskill in the art, the components of the uplink resource manager mayinvolve the physical (PHY) layer and/or the Media Access Control (MAC)layer of the transceiver 613. Transceiver 613 includes at least onereceiver 615 for receiving transmissions from various UEs within rangeof eNB 602 and at least one transmitter 616 for transmitting data andcontrol information to the various UEs within range of eNB 602.

The uplink resource manager executes instructions that control theoperation of transceiver 613. Some of these instructions may be locatedin memory 611 and executed when needed on processor 610. The resourcemanager controls the transmission resources allocated to each UE 601served by eNB 602 and broadcasts control information via the PDCCH. UE601 may receive TTD UL/DL configuration instructions from eNB 602.

Symbol processing circuitry 612 performs demodulation using knowntechniques. Random access signals are demodulated in symbol processingcircuitry 612. During transmission and reception of voice data or otherapplication data, receiver 617 may receive a random access signal from aUE 601. The random access signal is encoded to request a message sizethat is preferred by UE 601. UE 601 determines the preferred messagesize by using a message threshold provided by eNB 602.

Many modifications and other embodiments of the invention(s) will cometo mind to one skilled in the art to which the invention(s) pertainhaving the benefit of the teachings presented in the foregoingdescriptions, and the associated drawings. Therefore, it is to beunderstood that the invention(s) are not to be limited to the specificembodiments disclosed. Although specific terms are employed herein, theyare used in a generic and descriptive sense only and not for purposes oflimitation.

The invention claimed is:
 1. A method for operating a mobile device,comprising: establishing a connection to a first serving cell designatedas a primary serving cell (PCell); establishing a connection to a secondserving cell designated as a secondary serving cell (SCell), wherein theSCell uses a different duplex mode than the PCell; receiving subframescheduling messages for the SCell in a downlink subframe; and selectingan uplink subframe to send a scheduling message acknowledgement basedupon the duplex mode of the PCell, wherein the PCell and SCell duplexmodes are selected from a Frequency Division Duplex (FDD) mode and aTime Division Duplex (TDD) mode.
 2. The method of claim 1, wherein theprimary serving cell operates in FDD mode and the secondary serving celloperates in TDD mode.
 3. The method of claim 2, wherein a DownlinkControl Information (DCI) format scheduling downlink assignments oruplink grants on the TDD SCell does not include information in aDownlink Assignment index (DAI) field.
 4. The method of claim 1, whereina Downlink Control information (DCI) format scheduling an uplink granton a first serving cell operating in FDD mode contains information in aDownlink Assignment Index (DAI) field indicating the cumulative numberof scheduling message acknowledgements required for a second servingcell operating in TDD mode.
 5. The method of claim 1, wherein the mobiledevice is only capable of half-duplex operation.
 6. The method of claim5, wherein the primary serving cell operates in TDD mode and thesecondary serving cell operates in FDD mode, and further comprising:configuring the mobile device, to apply the same uplink/downlinkconfiguration of the TDD PCell for Hybrid Automatic Repeat Request(HARQ) acknowledgements corresponding to downlink assignments on aPhysical Downlink Shared Channel (PDSCH) of the FDD SCell.
 7. The methodof claim 1, wherein the mobile device is FDD-only and is operated on aTDD carrier, the method further comprising: configuring the mobiledevice with a restricted set of subframes to monitor for downlinkcontrol information scheduling downlink assignments on the TDD carrier.8. The method of claim 7, further comprising: indicating to the mobiledevice a set of subframes where a detected DL assignment on the POSCHcontains fewer than a maximum number of OFDM symbols in a subframe.
 9. Auser equipment device, comprising: a processor circuit configured to:establish a connection to a first serving cell operating in a FrequencyDivision Duplex (FDD) mode, the first serving cell designated as aprimary serving cell (Pcell); and establish a connection to a secondserving cell operating in a Time Division Duplex (TDD) mode, the secondserving cell designated as a secondary serving cell (SCell); a receivercircuit configured to receive downlink subframe scheduling messages forthe SCell; and a transmitter circuit configured to transmitacknowledgment messages on a Physical Uplink Control Channel of thePCell, or a transmitter circuit scheduled to transmit acknowledgmentmessages on a Physical Uplink Shared Channel, the acknowledgementmessages corresponding to the downlink subframe scheduling messagesreceived for the SCell.
 10. The user equipment of claim 9, wherein thesuhframe scheduling messages comprise a downlink data assignment, andwherein the acknowledgement messages comprise a positive or negativeHybrid Automatic Repeat Request acknowledgment (HARQ-ACK) for a PhysicalDownlink Shared Channel (PDSCH) transmitted on the TDD SCell, andwherein the HARQ-ACK message follows a HARQ-ACK timing format of the FDDPCell.
 11. The user equipment of claim 9, wherein when the receivercircuit detects a downlink assignment for the Physical Downlink SharedChannel (PDSCH) on the TDD SCell in a subframe n, the transmittercircuit transmits a Hybrid Automatic Repeat Request positive or negativeacknowledgment (HARQ-ACK) on the PUCCH of the FDD PCell or on an ULgrant in subframe n+4.
 12. The user equipment of claim 9, wherein whenthe receiver circuit detects a Downlink Control Information (DCI) formatscheduling an uplink grant on the FDD PCell, the transmitter circuittransmits one or more positive or negative acknowledgments according tothe information contained in a Downlink Assignment Index (DAI) field ofsaid DCI format.
 13. A user equipment device, comprising: a processorcircuit configured to: establish a connection to a first serving celloperating in a Time Division Duplex (TDD) mode, the first serving celldesignated as a primary serving cell (PCell); and establish a connectionto a second serving cell operating in a Frequency Division Duplex (FDD)mode, the second serving cell designated as a secondary serving cell(SCell); a receiver circuit configured to receive a Physical DownlinkShared Channel (PDSCH) message in a downlink subframe on the SCell; anda transmitter circuit configured to transmit an acknowledgment messagecorresponding to the received PDSCH message in a selected uplinksubframe.
 14. The user equipment of claim 13, wherein the transmittercircuit is configured to transmit acknowledgment messages on the PUCCHof the PCell.
 15. The user equipment of claim 13, wherein the downlinksubframe is subframe n, and the selected uplink subframe is subframen+k, where K≧4 and n+k is the first valid uplink subframe following thedownlink subframe.
 16. The user equipment of claim 13, wherein thetransmitter circuit is configured to transmit simultaneous PhysicalUplink Control Channel (PUCCH) transmissions on both the PCell andSCell.
 17. The user equipment of claim 13, wherein the transmittercircuit is configured to transmit time-multiplexed Physical UplinkControl Channel (PUCCH) transmission on the Pcell and SCell.
 18. Theuser equipment of claim 17, wherein the transmitter circuit transmits onPUCCH of the FDD SCell only if an uplink subframe on the FDD SCellcorresponds to a downlink subframe on the TDD PCell.
 19. The userequipment of claim 17, wherein the transmitter circuit transmits onPUCCH of the TDD PCell if said subframe is an uplink subframe on the TDDPCell.